It is typically necessary to control the level of contaminants in a cleanroom such that microelectronic device processing may be effectively carried out. An example of a common contaminant is floating dust. Other conditions within the cleanroom, such as those relating to noise, vibration, temperature, and light intensity, may also be controlled such that optimum processing conditions may be obtained.
Regulating dust levels, temperature, and humidity in a cleanroom is especially important during integrated circuit (e.g., semiconductor) device fabrication design layout. Design layout typically encompasses a number of operations relating to, for example, pattern formation in water fabrication, inspection, assembly/packaging, final testing, and quality testing. In particular, wafer fabrication usually involves repetitive process steps such as diffusion, exposure, development, etching, and diffusion. Specifically, equipment and materials involved in these process steps should not be contaminated in order to potentially obtain maximum microelectronic device production yield, precision, and reliability.
In a typical processing operation, air entering the cleanroom is usually filtered in order to attempt to remove the contaminants, and the air is then typically circulated throughout the cleanroom. Although it may be possible to achieve a certain level of air cleanliness, it is often extremely difficult to achieve an extremely high cleanliness level by only employing the above filtering system. Although the level of cleanliness attained by using a conventional filtering system may be adequate for certain processes, a higher degree of cleanliness is often desirable.
The presence of water-soluble contaminants, such as those resulting from wet fabrication processing, often adversely affect production yield and integrated circuit device operation. For example, the presence of water-soluble ionic materials on wafer surfaces may haze or blur the surfaces and distort corresponding photoresists. Moreover, the ionic materials are capable of functioning as dopants which can negatively impact diffusion processes containing these materials.
In view of the above, it would be desirable to control the level of water-soluble contaminants which may be present in a cleanroom. Conventionally, cleanroom cleanliness is typically controlled by monitoring the total number of particles present in the cleanroom atmosphere irrespective of the water solubility of the particles. The solubility of the particles is often measured by techniques involving the use of a as denuder, chemiluminescence, or fluoroluminescence.
FIG. 1 illustrates a conventional denuder. As shown, the denuder comprises an inlet 11 which may be connected to an inlet tube (not shown) capable of taking reference air for analysis from various directions. An impactor 12 is also present and is equipped with an impact plate 13. The denuder also includes a diffusion denuder 14, an after filter 15, and a sampling pump 16. Collected air typically collides with the impact plate 13 of the impactor 12 to thereby separate from the particles, and subsequently form microparticles which are not separated by impactor 12. More specifically, polar molecules such as SO.sub.2, NO.sub.2, or NH.sub.3 are separated inside the diffusion denuder 14 composed of stainless steel. The polar molecules are then typically supplied to the sampling pump through filter 15 such that a sample for analysis may be obtained. Notwithstanding any potential advantage, the conventional denuder typically is not able to separately analyze water-soluble materials which may be present in the reference air.
A conventional chemiluminescent method typically involves chemically reacting materials to be analyzed and then analyzing any light which may be emitted by the materials as a result of the chemical reaction typically initiated by using a photo-amplified tube. According to the chemiluminescent method, a radiation impulse (e.g., ultraviolet rays) is applied, and the material typically yields a luminsecence which is subsequently analyzed. The chemiluminescent method, however, may be disadvantageous in that only one component is typically analyzed at a time. Thus, the technique is often inefficient.
In addition to the above, samples have been collected and analyzed by conventional spectroscopic analyzers. In particular, these techniques may be carried out by using a Jar method, an Impinger method, and the like.
The Jar method typically involves exposing a jar containing deionized water to the atmosphere such that water-soluble contaminants are able to dissolve therein. The water-soluble contaminants are then subsequently analyzed. Although the structure and application of the jar are relatively simple, the above may be undesirable in that collection times are typically long. As a result, collection efficiency may be inaccurate. Although a post collection treatment is often employed in conjunction with this apparatus, it still may be difficult to obtain an accurate measurement of the contaminants.
The Impinger method typically involves spraying an air sample toward water or another liquid which is used as a collection source. The above operation is usually carried out by using a double tube or an gas collector impinger. The contaminants contained within the air are collected by the water or other liquid and then are subsequently analyzed. Although the apparatus used in the Impinger method is relatively simple, the method is potentially disadvantageous in that an additional treatment step is often required prior to contaminant analysis.
There is a need in the art for systems (apparatus) and methods for analyzing water-soluble contaminants which address the problems often associated with conventional analysis techniques.